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Fix segfault on infinite recursion in some cases

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This fixes a segfault on infinite function call recursion (rather than
infinite thunk recursion) by tracking the function call depth in
`EvalState`.

Additionally, to avoid printing extremely long stack traces, stack
frames are now deduplicated, with a `(19997 duplicate traces omitted)`
message. This should only really be triggered in infinite recursion
scenarios.

Before:

    $ nix-instantiate --eval --expr '(x: x x) (x: x x)'
    Segmentation fault: 11

After:

    $ nix-instantiate --eval --expr '(x: x x) (x: x x)'
    error: stack overflow

           at «string»:1:14:
                1| (x: x x) (x: x x)
                 |              ^

    $ nix-instantiate --eval --expr '(x: x x) (x: x x)' --show-trace
    error:
           … from call site
             at «string»:1:1:
                1| (x: x x) (x: x x)
                 | ^

           … while calling anonymous lambda
             at «string»:1:2:
                1| (x: x x) (x: x x)
                 |  ^

           … from call site
             at «string»:1:5:
                1| (x: x x) (x: x x)
                 |     ^

           … while calling anonymous lambda
             at «string»:1:11:
                1| (x: x x) (x: x x)
                 |           ^

           … from call site
             at «string»:1:14:
                1| (x: x x) (x: x x)
                 |              ^

           (19997 duplicate traces omitted)

           error: stack overflow
           at «string»:1:14:
                1| (x: x x) (x: x x)
                 |              ^
This commit is contained in:
Rebecca Turner 2023-12-15 11:52:21 -08:00
parent a21c762dab
commit 7434caca05
No known key found for this signature in database
12 changed files with 358 additions and 4 deletions
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18
src/libexpr/eval.cc
View file

@ -1505,9 +1505,27 @@ void ExprLambda::eval(EvalState & state, Env & env, Value & v)
v.mkLambda(&env, this);
}
namespace {
/** Increments a count on construction and decrements on destruction.
*/
class CallDepth {
size_t & count;
public:
CallDepth(size_t & count) : count(count) {
++count;
}
~CallDepth() {
--count;
}
};
};
void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const PosIdx pos)
{
if (callDepth > evalSettings.maxCallDepth)
error("stack overflow; max-call-depth exceeded").atPos(pos).template debugThrow<EvalError>();
CallDepth _level(callDepth);
auto trace = evalSettings.traceFunctionCalls
? std::make_unique<FunctionCallTrace>(positions[pos])
: nullptr;